1. Field of the Invention
The invention relates to a plastic contact tube or ferrule and to fastening an end of an optical fiber made of plastic material in the contact tube (or ferrule).
2. Description of the Prior Art
It is known from U.S. Pat. No. 5,421,928 to fix an optical fiber end in a tube (ferrule) in such a way that the end projects beyond the end face of the tube, then to cut-off the end by means of a laser and subsequently to polish the end face of tube and optical fiber.
It is known from JP 58-108508 A to fix a fiber end in a tube by pushing against an end face. The fiber is then provisionally retained in the tube. The fiber end is heated and thus cleaned and smoothed, whereupon the fiber is fixed to the tube.
It is known from U.S. Pat. No. 4,510,005 to introduce a fiber end into a tube and to press the end against a highly polished surface. Heating of this end surface causes the surface of the fiber end to melt and to adapt itself to the highly polished surface. Simultaneously with the heating, it is possible to activate an adhesive located between the fiber and the tube and thus fix the fiber in the tube.
It is also known from U.S. Pat. No. 4,695,124 to fuse an optical fiber within a tube by means of heat where the fiber and tube consist of plastic material.
An optical fiber end made of plastic can be fused with a plastic tube in a particularly simple and inexpensive manner. A method of this type can be carried out, for example, by heat treatment. A drawback of this method is that spatially targeted application of heat to a specific location is very difficult.
Starting from this state of the art, the object of this invention is to provide for reliably fastening an end of a plastic optical fiber in a ferrule or tube made of plastic material. Additionally, it is an object to provide a suitable plastic ferrule or tube.
A defined position of the optical fiber end in the contact tube is provided during introduction of the optical fiber end into the plastic tube. The defined position is achieved in that the optical fiber end is positioned relative to the end face of the plastic tube. The optical fiber end which is to be introduced and which comprises an outer sheath is finished at the end face and freed from the outer sheath over a predetermined length. Positioning with respect to the end face of the contact tube takes place during introduction of the optical fiber end into the contact tube. It is immaterial whether the contact tube is formed in one part and the optical fiber end is inserted from one end or whether the contact tube consists of two shells which are joined together.
The forces for extraction of the optical fiber end from the contact tube can be increased by fusing the optical fiber end with the contact tube. This can be effected in the region of the outer sheath as well as in the region of the primary sheath or core of the optical fiber. Particularly high retention forces are achieved because the contact tube and the optical fiber are fused together along both the outer sheath and the primary sheath or core. It is particularly advantageous to fuse the primary sheath or core to the contact tube as a change in the end face position of the optical fiber due to differing thermal expansion can be avoided.
It is also particularly advantageous if the wall of the bore of the contact tube is structured with ribs or teeth that engage the optical fiber because increased extraction forces can also be achieved in this way. The structure not only improves clamping of the optical fiber but also can be useful to establish fusion at defined points between the optical fiber and the contact tube when the contact tube is charged with ultrasound.
It is also particularly advantageous to divide the contact tube longitudinally, at least in certain regions, into two half shells which are later joined together by ultrasound with the fiber therebetween. The optical fiber will be compressively clamped between the two half shells. The half shells can also be joined together by corresponding catch/latch structure. Structures on the wall of the bore where the optical fiber is positioned can also be produced particularly easily owing to the forming of the contact tubes as two half shells. Therefore, the structure can have almost any form, for example a rib-shaped, waffle-shaped, pyramid-shaped or cylindrical cone-shaped configurations.
It is particularly advantageous that, with a contact tube consisting of two half shells, the optical fiber will not only be clamped but also welded to the shells by ultrasound. A particularly advantageous fastening of the optical fiber end in the contact tube is achieved if the optical fiber end is clamped along the region of the outer sheath and then ultrasonically welded to the contact tube in the region of the primary sheath or core.
A further feature is that the two half shells can include centering and positioning pins or corresponding recesses for the relative positioning thereof when the shells are being joined together.
It is also particularly advantageous if the half shells comprise, in the region of the faces which are joined together, welding ribs as ultrasonic guides to simplify welding by directing the ultrasound energy.
Finally, it is possible for the invention to be constructed as a single-part contact tube, the structure on the wall of the bore can have the form of a thread or of longitudinal ribs. The tube can then be ultrasonically welded to the optical fiber end, but additional clamping does not occur only the deformation of the external geometry of the optical fiber during insertion.
It is also particularly advantageous if two types of contact shell are provided. The first contact shell being formed with a receiving region at an end face. The second contact shell having an end face being formed in such a way that it can be introduced into the receiving region of the first contact shell. The two plastic contact shells in cooperation with respective optical fiber ends can mate in the manner of a socket and a pin contact.
It is also particularly advantageous to design the half shells hermaphroditically. An inexpensive contact tube, which is simple to produce, is thus provided.